To prevent solid particles suspended in a fluid from being discharged at the same time as the fluid, the centrifugal force is generally used, for example by means of cyclones or by making both the fluid and the solid particles rotate inside the chamber that contains them, which chamber may itself be rotary.
Generally speaking, since the rotation speed of the fluid and the solid particles is low, close to and along the fluid discharge tube, the smallest solid particles are driven to the inside of said discharge tube. To prevent solid particles from being so driven, a rotary duct may be used, such as that described in Patent Application PCT/EP2007/053941 filed by TOTAL PETROCHEMICALS RESEARCH FELUY, on 23, Apr. 2007, in the name of the same inventor. However, the vacuum, which is necessary for overcoming the centrifugal force generated by said rotary chamber and for sucking up and discharging the fluid through its openings inside the fixed central fluid discharge tube, may also suck up the fluid and the solid particles in suspension in this fluid through the generally narrow space between said rotary chamber and the walls of said fixed central fluid discharge tube.